Electrical single-axle drives are often structured with multiple stages. They consist of a control facility, a motor control unit and an electric motor. In normal mode the control facility receives setpoint values from a higher-order controller in a clocked manner. It also receives actual values. The received setpoint and actual values can be position, speed or torque values. The control facility uses the setpoint values and actual values to determine setpoint current values and transmits these to the motor control unit. The motor control unit also receives an actual current value and uses the setpoint current value and the actual current value to determine activation signals for electronic circuit breakers, by way of which the electric motor is connected to an energy supply. The electronic circuit breakers are generally integrated in the motor control unit.
Instead of an individual electric motor, a group of electric motors can also be present in an electrical single-axle drive, if all the electric motors in the respective group are always activated in the same manner.
Electrical multiple-axle drives are structured in the same manner as electrical single-axle drives. However they have a number of electric motors and a number of motor control units, with each electric motor being activated individually by a control facility common to the electric motors. Each motor control unit is generally configured as a dedicated structural unit. However the motor control units can alternatively be combined to form a common structural unit—optionally also in conjunction with the control facility.
Axle drives can generally not only be operated in normal mode but also in safety mode. For example an axle drive can be switched to zero current, braked actively to a standstill and then switched to zero current, braked actively to a standstill and then kept actively at a standstill or operated at limited speed. Other states are also possible.
In order to be able to identify whether safety mode should be assumed and which safe state (see examples above) should be assumed in some instances, corresponding switching signals must be supplied to the control facility and/or the motor control units. In some instances feedback signals must also be output by the control facility and/or the motor control units.
It is known in the prior art that the corresponding switching signals can be supplied to each motor control unit by way of connections to be wired individually (e.g. screw terminals or cage clamp terminals). Feedback signals that have to be emitted in some instances are emitted in a similar manner. This type of connection is very flexible but it is time-consuming and error-prone. In particular the time outlay required to connect the required signal lines manually increases in a linear manner (or more steeply) with the number of drives. This is also the case when the same signal (e.g. an emergency stop signal) is to trigger the same safety response in a number of drives, which can be activated independently of one another in normal mode.
To reduce the wiring outlay it is known that the motor control unit can be connected to a safe bus (e.g. PROFIsafe) and the switching signals—optionally also the feedback signals—can be transmitted by way of the bus. However, this solution requires the deployment of a fail-safe controller, which in many instances is not possible and is also technically complex.
In the case of a component conductor connection the respective safety function per se must also be integrated in the motor control units. The motor control unit must therefore be able to identify and generate the required safety state based on the switching signals supplied to it.
It is already known that the motor control unit can be supplied with a prefabricated multipole interface, onto which a plug-type module can be plugged. In this embodiment the plug-type module is responsible for converting the switching signals supplied to the plug-type module to the corresponding control signals to trigger the respective safety function in the motor control unit. The output signals emitted by the plug-type module are determined based on logic functions, which incorporate both the input signals, supplied to the plug-type module and internally stored states.
However it is not possible to resolve the underlying problem of the prior art even with plug-type modules, since the wiring outlay remains the same. It is only displaced from the motor control units to the plug-type modules.
A control module for a number of controllable drive axles of a printing machine is known from DE 103 44 070 A1. The control module has a drive computation unit, which is suitable for controlling a number of drive axles as a function of predetermined activation signals. The control module also has a monitoring computation unit, which is suitable for monitoring and in some instances preventing the movement of the drive axles as a function of predetermined safety data. The monitoring computation unit appears to be an integral part of the control module. The input signals, which the monitoring computation unit uses to determine whether the drives have to be switched to a safe state, are supplied to the control module by way of a bus connection.
A device for monitoring safety for protection facilities is known from EP 0 465 710 A1, being structured in a module manner from a number of units, with the individual units being connected electrically to one another by plug-type contact means and being mounted mechanically side by side.